1. Field of the Invention
The present invention relates to a demineralizer of the primary coolant system and a method for purifying the primary cooling water in the pressurized-water reactor power plant.
2. Description of the Related Art
In the pressurized-water power plant, there are two major systems utilized to convert the heat generated in the nuclear reactor into electrical power. The first one, the primary system, transfers the heat from the reactor to the second one, the secondary system. The heat generates steam in the steam generator in the secondary system, which is transferred to the main turbine, where it generates electricity. After going through the low pressure turbine, the steam is routed to the main condenser. Cool water flowing through tubes in the condenser removes heat from the steam, allowing the steam to condense. The water is then pumped back to the steam generator for reuse. In order to perform these functions, there are approximately one hundred supporting units in the primary and secondary systems. Among them, the demineralizer of the primary coolant system is the one that is essential.
Various demineralizers are installed in the primary coolant systems, a chemical and volume control system (CVCS), a boric acid recovery system (BRS) and a spent fuel pit water cooling system (SFPCS), for example, to remove impurities such as chloride ion and fluoride ion, fission products such as 131I, and corrosion products of 58Co, 60Co, nickel, iron and the like contained in the primary cooling water.
For the purpose of achieving such purification of the primary cooling water, in each of the CVCS, the BRS and the SFPCS, a mixed bed demineralizer is installed. Among the inventions relating to the operation of the mixed bed demineralizer, an invention relating to the mixing ratio between a cation exchange resin and an anion exchange resin has been reported in Japanese Patent Laid-Open No. 2005-3598. It should be noted that in the demineralizer of the primary coolant system, a gel- and OH-form anion exchange resin has been generally used as the anion exchange resin.
Boric acid is added to the primary cooling water, for the purpose of controlling the critical state of the reactor fuel. In particular, during a periodic inspection or fuel exchange, the boron concentration of the primary cooling water is increased so as to maintain the fuel at a subcritical state. Then, at the resumption of the operation of the PWR power plant, the primary cooling water, which has a boron concentration higher than that in the normal operation, goes threw the demineralizer and conducts boric acid exchange. In recent years, for the purpose of improving the power generation efficiency and the operation rate, the use of high burnup fuel has been considered. When such high burnup fuel is used, it will be necessary to further increase the boron concentration of the primary cooling water at the halt of the operation of the PWR power plant.